This invention relates to a vehicle suspension system designed to provide continuous vertical orientation of the central plane of the ground wheel while the suspension allows the wheel to move vertically relative to the frame of the vehicle.
Conventional suspension systems particularly for the front wheels of a road vehicle generally provide a suspension arm pivotally mounted on a suitable frame member at a position inwardly of the wheel towards a centre line of the vehicle. At an outer end of the pivot arm is provided a wheel support or coupling member with the wheel being carried on a cantilever arm which extends outwardly from the coupling member into the hub of the wheel and providing a shaft carrying bearings on which the wheel is mounted for rotation around the wheel axis.
In many cases, pivotal movement of the suspension arm causes the wheel axis to pivot so that a central plane of the wheel no longer remains vertical but twists about an axis longitudinal to the forward movement of the vehicle, thus changing the camber angle of the wheel.
In order to steer the wheel it is generally necessary to provide ball joints which allow the cantilevered shaft to pivot about a substantially vertical axis positioned inwardly of the wheel toward the centre line of the vehicle. This pivot action causes the wheel to move forwardly and rearwardly in the steering action and causes significant changes within the vehicle geometry as the steering takes place.
As the movement of the suspension changes the orientation of the central plane of the wheel, it also changes the orientation of the periphery of the tire relative to the horizontal surface of the ground. The tire therefore must deform to maintain as much flat surface of tire on the ground as possible while the angle of the rim supporting the tire varies. Attention has been given in recent years to reducing the profile of the tire but this is limited by the fact that the tire must have sufficient ability to deform to accomodate these changes in angle of the rim relative to the ground.
The steering and suspension system in the conventional system is relatively complex and must be manufactured using relatively heavy components in view of the significant forces involved in the cantilever support arrangement.
The geometry of the steering suspension system also provides complication in the alignment so that careful checking of the alignment is necessary and in the event that the alignment is disturbed, this can rapidly lead to damage to the tires.
The conventional steering and suspension geometry has therefore all of the above problems and yet remains substantially unaltered after many years of development.
Racing cars often use a somewhat different suspension system which attempts more vigorously to retain the periphery of the tire permanently horizontal in view of the fact that the traction between the tire and the ground is significantly more important during racing. The suspension system therefore includes often a parallelogram type linkage so that the wheel hub mounted inside the drum type rim stays substantially vertical while moving upwardly and downwardly in the suspension action. This system however provides a very limited amount of suspension movement which is suitable for racing vehicles but is not suitable for conventional road vehicles where the roadway is less than perfect and the passengers expect more comfort.